1. Field of the Invention
The present invention relates to a hot melt ink composition comprising a copolyester. The present invention further relates to a hot melt ink composition comprising a copolyester mixture. The present invention also relates to a process for preparing a copolyester and use of a hot melt ink comprising a copolyester in a ink jet printing process.
2. Description of Background Art
Copolyesters and hot melt ink compositions comprising a copolyester are known in the art. A hot melt ink composition is an ink composition that is solid at room temperature and liquid at elevated temperature. Inks of this kind, are also known as meltable inks or phase change inks. Known hot melt ink compositions comprise for example a crystalline material, a colorant and a binder.
In a printing device, for example an ink jet printer, the ink is melted and transferred to substantially closed ink ducts which lead at one end into an orifice. As a result of a sudden pressure rise in the duct, produced for example by rapidly reducing the volume of the ink duct or rapidly evaporating some of the ink in the duct, a drop of ink may be ejected from the duct through the orifice. In this way, an image may be built up from individual ink drops on a receiving medium. Hot melt inks contain a carrier material with a melting point higher than room temperature. The ink may melt in the printing device. Hot melt inks of this kind have the advantage that they set rapidly on the receiving medium, so that the print quality is less dependent on the type of receiving medium.
However, a disadvantage of the hot melt ink compositions known in the background art is the fact that images formed using these hot melt ink compositions often show low print robustness after printing on a recording medium.
U.S. Pat. No. 6,682,587 B2 discloses polyesters and copolyesters, as well as their use in hot melt inks. The esters and copolyesters described are esters from a dihydroxyl alcohol and an aromatic carboxylic acid.
U.S. Pat. No. 6,280,510 B1 discloses an ink composition for a meltable ink comprising a diester from a 2,2-biphenol compound (a dihydroxyl alcohol) and an aromatic acid. U.S. Pat. No. 6,280,510 B1 further discloses that use of this ink composition provides images showing improved print robustness. However, regarding print robustness, there is room for improvement.